The present invention relates to an illumination apparatus, and specifically relates to an illumination apparatus in which a plurality of OLEDs (Organic Light Emitting Diodes) is arranged.
When a plurality of singular OLED devices are made to be arrayed in a coupling pattern, the OLED devices are generally coupled to each other in a serial connection mode, instead of a parallel connection mode, in order to avoid such troubles that, when plural OLED devices are coupled to each other in the parallel connection mode, the electric currents respective flowing into the plural OLED devices are not the same and this causes variations between the luminance levels of the plural OLED devices, and if one of them generates a malfunction of the short circuit, all of the OLED devices becomes incapable of emitting light, etc.
Further, conventionally well-known is such an illumination apparatus that employs the plurality of singular OLED devices, which are coupled to each other in the serial connection mode, as the light source, and that makes them emit light by supplying the electric current acquired by applying the half-wave rectifying operation to the alternate electric current (hereinafter, also referred to as AC, for simplicity) fed from the commercial power source (for instance, refer to Tokkai 2004-234868 (Japanese Patent Application Laid-Open Publication)).
Still further, conventionally well-known is such another illumination apparatus that includes a plurality of OLED units, each of which is configured by coupling the singular OLED devices to each other in the serial connection mode, so as to make it possible to vary the brightness thereof by employing the AC for driving the OLED units coupled to the commercial power source, and by increasing and decreasing the number of OLED units that are currently turned ON, while making each of the OLED units turn ON or OFF as needed (for instance, refer to Tokkai 2004-134385 (Japanese Patent Application Laid-Open Publication)).
Yet further, conventionally well-known is such still another illumination apparatus that makes it possible to increase and decrease the brightness of the light source constituted by a single OLED, by employing controlling method for changing a value of direct electric current (hereinafter, also referred to as DC, for simplicity) voltage at the time of the high luminance mode, while employing the PWM (Pulse Width Modulation controlling method for modulating the DC voltage into the width-modulated pulses at the time of the low luminance mode (for instance, refer to Tokkai 2007-251036 (Japanese Patent Application Laid-Open Publication)).
However, with respect to the illumination apparatus set forth in Tokkai 2004-234868, there has been such a problem that, although it is possible to simplify the configuration of the driving power source, it is impossible to increase and decrease the luminance level of the light source (hereinafter, also referred to as a dimming control operation), since the purpose of Tokkai 2004-234868 is to make the illumination apparatus keep a constant brightness.
Further, with respect to the illumination apparatus set forth in Tokkai 2004-134385, since the switching member is required for every one of the plural OLED units, a large number of combinations of the OLED units and the switching members becomes necessary for smoothing the transition of the brightness changing control. Accordingly, there have been such problems that the configuration thereof becomes complicated considerably and is hardly brought into the practical use, while, when the number of combinations of the OLED units and the switching, members is made to decrease, it becomes impossible to conduct a sufficient dimming control operation.
Still further, with respect to the illumination apparatus set forth in Tokkai 2007-251036, in which the dimming control operation of the light source, constituted by a plurality of OLED devices, is achieved by conducting the controlling operation for changing the value of the DC voltage at the time of the high luminance operating mode, there have arisen such problems that a slight voltage change causes a large amount of brightness change due to the fact that the brightness versus voltage characteristic of the OLED is nonlinear, as shown in FIG. 11, resulting in the deterioration of the accuracy of the dimming control operation, and the range of the brightness differences between the plural OLEDs becomes large, due to the variations between the individual characteristics respectively corresponding to the plural OLEDs concerned.
In this connection, it has been revealed in the process of achieving the present invention through the various kinds of considerations, conducted by the present inventor, that the illumination apparatus set forth in Tokkai 2007-251036 have had such the problems that the accuracy of the dimming control operation is deteriorated at the time of the high luminance operating mode even when either the voltage value or the duty ratio of the pulse is made to selectively changed, and the range of the brightness differences becomes large, due to the variations between the individual characteristics.